[pstl][libc++] Provide uglified header names for interface headers

For the few (currently four) headers that make up the PSTL's interface
to other Standard Libraries, provide a stable uglified header file that
can be included by those Standard Libraries.

We can then more easily change the internal organization of the PSTL
without having to change the integration with Standard Libraries.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@368088 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed